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Friday, March 9, 2012

I'm dissoluting! Dissoluting!

I wonder what the pH of the water in that bucket was...

Last Tuesday we learned about ocean acidification and what that phrase means. The uptake of atmospheric CO2 is creating more hydrogen ions in the ocean which lowers the pH, therefore making the ocean more acidic. So what does all this crazy acidification mean for calcium carbonate-encrusted crustaceans? Perhaps something like this:

oh dear.

Well, maybe that's an overdramatization; crabs aren't melting in ocean water with lower pH. But they are developing differently. There are a few studies going on here in Alaska looking at larval development in different pH water treatments. One such study by NOAA out in Kodiak (pdf poster here) looked at survival, growth, and calcium uptake of larval blue king crabs in pH treatments of ambient (normal levels in Auke Bay here in Juneau was 7.94 in 2010), minus 0.3 below ambient pH, and minus 0.5 below ambient pH. Sure enough, growth decreased in the lower pH treatments shown by an overall decrease in % dry mass.

"We're not growing! Oh, what a petri dish!"

Why is the development different if the acidified ocean water isn't actually melting the crabs' carapaces? Animals have the ability to regulate their internal acid-base relationship, and crabs do so by taking advantage of their calcium carbonate exoskeleton: when pH is lowered due to high levels of hydrogen ions, crabs can increase carbonate ions to bind with the hydrogen ions (thus making bicarbonate ions) through shell dissolution.

above is a crab with low pH due to all those pesky hydrogen ions

by using the calcium carbonate in its shell, it can get rid of some of those hydrogen ions by making bicarbonate ions

a dissolving shell results in less hydrogen ions and a higher pH (yay!)
plus an increase in calcium and bicarbonate ions

More research is in the works: UAF student Raphaelle Descoteaux is measuring any morphometric deformities in larval Tanner (Chionoecetes bairdi) and Dungeness (Metacarcinus magister)crabs that may occur in acidified seawater. We'll hear from her in a future Ask A Grad Student post, so stay tuned!